mass shooters... gravitate to assault rifles
Absolutely false. The vast majority of "mass shootings" are with handguns.> We have different definitions of mass shooters.
You're almost certainly talking about high profile shooting incidents with broad media coverage, that drive what is essentially a moral panic.
Parent comment is referring to incidents where 3+ people get shot, which often do not make the national and international media, and are predominately carried out with handguns.
The shootings last August that got a lot of attention are a great example. Couple of back-to-back mass shooting incidents in TX and Ohio got a lot of press... even though just the week before something like 34 people got shot in Chicago over the course of 2 days; hardly a word in the press outside of Chi-town.
You group the two in order to dilute the focus of anti-gun violence advocacy, but you're given away by how little you care about instances of the latter definition otherwise. If "mental healthcare" is your panacea, it won't help non-suicide handgun violence. You know that, and I know that, and it's then perplexing why you would think we wouldn't notice.
As an addendum, I have to imagine that GRAs enjoy this debate, because as long as we're stuck on it, we don't have to talk about how access to handguns increases the successful suicide attempt rate.